Thank you, Rounsworth.

I believe, however, that minumum wall thickess has not much to do with the matter. Apparently, it is the chamber area where the walls had to be made thicker to withstand nitro pressure.

So, the measurements I'm looking for are 1) at the breech; 2) at the end of chamber; 3) at the end of forcing cone.

This is especially relevant for the guns which had the chamber lenghened - you've got to know if there's enough wall left, but how much is enough?